Exercise machine

ABSTRACT

An exercise machine includes: a flywheel mounted rotatably to a support frame; a crank wheel mounted rotatably to the support frame; a transmission belt trained on the flywheel and the crank wheel; and a pressurizing wheel mechanism including a mounting seat mounted to the support frame, upper and lower pressure wheel units provided pivotally on the mounting seat, and upper and lower limiting members mounted to the mounting seat. The upper and lower pressure wheel units respectively have upper and lower pressure wheels biased to move in first and second directions so as to press and tense upper and lower segments of the transmission belt that extend between the flywheel and the crank wheel. The upper and lower limiting members limit movement of the upper and lower pressure wheel units in directions opposite to the first and second directions, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an exercise machine, more particularly to an elliptical trainer.

2. Description of the Related Art

As shown in FIG. 1, a conventional elliptical trainer 10 includes a base 11, a first support frame 12 mounted proximate to and extending upwardly from a front end of the base 11, two swing handles 13 (only one is shown) mounted rotatably to the first support frame 12, an electric motor 14 mounted to the front end of the base 11, a second support frame 15 mounted to the base 11 proximate to a rear end of the base 11, a flywheel unit 16 mounted rotatably to the second support frame 15 and coupled to the electric motor 14 for assisting in rotation of the flywheel unit 16, a crank wheel unit 17 mounted rotatably to the second support frame 15 and disposed rearward of the flywheel unit 16, a pressure wheel unit 18 provided pivotally on the second support frame 15, and two pedal assemblies 19 (only one is shown), each of which is mounted pivotally to the crank wheel unit 17 and a respective one of the swing handles 13. The flywheel unit 16 includes large and small flywheels 161, 162, and first and second transmission belts 163, 164. The crank wheel unit 17 includes a crank wheel 171, and two cranks 172 mounted pivotally to a center of the crank wheel 171 and to a respective one of the pedal assemblies 19 at opposite ends thereof. The first transmission belt 163 is trained on the large flywheel 161 and the electric motor 14. The second transmission belt 164 is trained on the small flywheel 162 and the crank wheel 171 such that rotation of the small flywheel 162 results in rotation of the crank wheel 171. The crank wheel 171 drives the cranks 172 to rotate, which in turn rotates the pedal assemblies 19 in swinging motion.

Moreover, when the crank wheel 171 is rotated in a counterclockwise direction by rotation of the flywheel unit 16, which is driven by the electric motor 14, an upper segment of the second transmission belt 164 is tensed and a lower segment of the second transmission belt 164 becomes loose. However, when the user pedals to rotate the crank wheel 171 counterclockwise through the motion of the pedal assemblies 19, the lower segment of the second transmission belt 164 is tensed and the upper segment of the second transmission belt 164 becomes loose. Having a loose upper segment in the second transmission belt 164 easily affects overall transmission of rotation performed by the second transmission belt 164. Therefore, the pressure wheel unit 18 serves the purpose of pressing and tensing the upper segment of the second transmission belt 164. The pressure wheel unit 18 includes a moving plate 181 having a first end mounted pivotally to the second frame support 15, a biasing member 183 coupled to a second end of the moving plate 181 opposite to the first end, and a pressure wheel 182 mounted rotatably to the moving plate 181 between the first and second ends. The biasing member 183 biases the pressure wheel 182 toward the upper segment of the second transmission belt 164.

Although the pressure wheel unit 18 is capable of pressing and tensing the upper segment of the second transmission belt 164, some drawbacks still exist that require improvement. Rotation of the crank wheel unit 17 is not only affected by drive of the electric motor 14, but is also affected by the user's weight. In other words, the crank wheel 171 is connected to the pedal assemblies 19 via the cranks 172 such that the user's weight on the pedal assemblies 19 exerts a downward force on the cranks 172 and the crank wheel 171. When one of the cranks 172 is rotated from position (I′) to position (II′), the user's weight on the corresponding pedal assembly 19 exerts an auxiliary force that tends to rotate the crank wheel 171 in the counterclockwise direction such that the upper segment of the second transmission belt 164 is loose and the lower segment of the second transmission belt 164 is tense. Under this circumstance, the pressure wheel unit 18 is capable of pressing and tensing the upper segment of the second transmission belt 164 so as to ensure smooth transmission of rotation performed by the second transmission belt 164. However, when the other one of the cranks 172 is moved from the position (II′) to the position (I′), the user's weight on the corresponding pedal assembly 19 can exert an auxiliary force that tends to rotate the crank wheel 171 in a clockwise direction. If the drive of the electric motor 14 is unable to overcome this auxiliary force, then the auxiliary force would result in tension in the upper segment of the second transmission belt 164 and slackening in the lower segment of the second transmission belt 164. Since no component is provided for tensing the lower segment, slippage of the second transmission belt 164 can easily occur such that transmission of power is disturbed, resulting in hindering or stopping of movement of the pedal assemblies 19.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide an exercise machine that eliminates slippage of a transmission belt thereof.

According to one aspect of the present invention, there is provided an exercise machine that includes a base, a support frame, a flywheel unit, a crank wheel unit, a transmission belt, and a pressurizing wheel mechanism. The support frame is mounted to the base. The flywheel unit is mounted rotatably to the support frame. The crank wheel unit is mounted rotatably to the support frame. The transmission belt is trained on the flywheel unit and the crank wheel unit. The pressurizing wheel mechanism includes a mounting seat, upper and lower pressure wheel units, and upper and lower limiting members. The mounting seat is mounted to the support frame, and is disposed proximate to the transmission belt. The upper pressure wheel unit is provided pivotally on the mounting seat, and has an upper pressure wheel biased to move in a first direction so as to press and tense an upper segment of the transmission belt that extends between the flywheel unit and the crank wheel unit. The lower pressure wheel unit is provided pivotally on the mounting seat, and has a lower pressure wheel biased to move in a second direction so as to press and tense a lower segment of the transmission belt that extends between the flywheel unit and the crank wheel unit below the upper segment. The upper limiting member is mounted to the mounting seat to limit movement of the upper pressure wheel unit in a direction opposite to the first direction. The lower limiting member is mounted to the mounting seat to limit movement of the lower pressure wheel unit in a direction opposite to the second direction.

According to another aspect of the present invention, there is provided an exercise machine that includes a base, a support frame, a flywheel unit, a crank wheel unit, a transmission belt, and a pressurizing wheel mechanism. The support frame is mounted to the base. The flywheel unit is mounted rotatably to the support frame. The crank wheel unit is mounted rotatably to the support frame. The transmission belt is trained on the flywheel unit and the crank wheel unit. The pressurizing wheel mechanism includes a mounting seat, a pressure wheel unit, and a limiting member. The mounting seat is mounted to the support frame, and is disposed proximate to the transmission belt. The pressure wheel unit is provided pivotally on the mounting seat, and has a pressure wheel biased to move in a first direction so as to press and tense a segment of the transmission belt that extends between the flywheel unit and the crank wheel unit. The limiting member is mounted to the mounting seat to limit movement of the pressure wheel unit in a direction opposite to the first direction.

According to yet another aspect of the present invention, there is provided an exercise machine that includes a base, a support frame, a flywheel unit, a crank wheel unit, a transmission belt, and a pressurizing wheel mechanism. The support frame is mounted to the base. The flywheel unit is mounted rotatably to the support frame. The crank wheel unit is mounted rotatably to the support frame. The transmission belt is trained on the flywheel unit and the crank wheel unit. The pressurizing wheel mechanism includes a mounting seat, and upper and lower pressure wheel units. The mounting seat is mounted to the support frame, and is disposed proximate to the transmission belt. The upper pressure wheel unit is provided pivotally on the mounting seat, and has an upper plate holding an upper pressure wheel biased to move in a first direction so as to press and tense an upper segment of the transmission belt that extends between the flywheel unit and the crank wheel unit. The lower pressure wheel unit is provided pivotally on the mounting seat, and has a lower plate holding a lower pressure wheel biased to move in a second direction so as to press and tense a lower segment of the transmission belt that extends between the flywheel unit and the crank wheel unit below the upper segment.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiment with reference to the accompanying drawings, of which:

FIG. 1 is a schematic diagram of a conventional elliptical trainer;

FIG. 2 is a perspective view of the preferred embodiment of an exercise machine according to the present invention;

FIG. 3 is a fragmentary schematic view of the preferred embodiment;

FIG. 4 is a fragmentary top view of the preferred embodiment;

FIG. 5 is an assembled schematic view of a pressurizing wheel mechanism according to the preferred embodiment;

FIG. 6 is a sectional view of the pressurizing wheel mechanism according to the preferred embodiment, taken along line VI-VI in FIG. 4;

FIG. 7 is a schematic side view of the preferred embodiment, illustrating the preferred embodiment in a state of use;

FIG. 8 is a fragmentary schematic view of the preferred embodiment, illustrating counterclockwise rotational force resulting from a user's weight exerted on a crank wheel unit;

FIG. 9 is a schematic view of the pressurizing wheel mechanism when the preferred embodiment is under the state shown in FIG. 8;

FIG. 10 is a fragmentary schematic view of the preferred embodiment, illustrating clockwise rotational force resulting from the user's weight exerted on the crank wheel unit;

FIG. 11 is a schematic view of the pressurizing wheel mechanism when the preferred embodiment is under the state shown in FIG. 10; and

FIG. 12 is a schematic side view of the preferred embodiment similar to FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 2 and FIG. 3, the preferred embodiment of an exercise machine according to the present invention includes a base 21, an electric motor 22, a first support frame 23, a flywheel unit 24, a crank wheel unit 25, first and second transmission belts 26, 27, a pressurizing wheel mechanism 30, and two pedal assemblies 50 (only one is shown in FIG. 2). The first support frame 23, the flywheel unit 24, the crank wheel unit 25, the first and second transmission belts 26, 27, and the pressurizing wheel mechanism 30 are concealed in a housing 20.

As shown in FIG. 3 and FIG. 4, the electric motor 22 is mounted to a front end of the base 21. The first support frame 23 is mounted to the base 21 proximate to a rear end of the base 21. The fly wheel unit 24 is mounted rotatably to the first support frame 23, and is coupled to the electric motor 22 for assisting in rotation of the flywheel unit 24. The crank wheel unit 25 is mounted rotatably to the first support frame 23, and is disposed rearward of the flywheel unit 24. In particular, a motor shaft 221 extends outwardly of the electric motor 22. The flywheel unit 24 includes concentric large and small flywheels 241, 242. The crank wheel unit 25 includes a crank wheel 251, and two cranks 252 (only one is shown in FIG. 3) coupled pivotally to a center of the crank wheel 251 and to a respective one of the pedal assemblies 50 at opposite ends thereof. The first transmission belt 26 is trained on the motor shaft 221 and the large flywheel 241 of the flywheel unit 24 such that rotation of the motor shaft 221, i.e., rotation of the electric motor 22, drives the large flywheel 241 rotatably. The second transmission belt 27 is trained on the small flywheel 242 of the flywheel unit 24 and the crank wheel 251 of the crank wheel unit 25 such that rotation of the small flywheel 242 drives the crank wheel 251 rotatably.

As shown in FIG. 5 and FIG. 6, in combination with FIG. 3 and FIG. 4, the pressurizing wheel mechanism 30 includes a mounting seat 31, upper and lower pressure wheel units 32, 33, and upper and lower limiting members 34, 35. Referring back to FIG. 3, the mounting seat 31 is mounted to the first support frame 23, and is disposed proximate to the second transmission belt 27. The upper and lower pressure wheel units 32, 33 are provided pivotally on the mounting seat 31. The upper pressure wheel unit 32 has an upper pressure wheel 322 biased to move in a first direction (A) so as to press and tense an upper segment 271 of the second transmission belt 27 that extends between the flywheel unit 24 and the crank wheel unit 25. The lower pressure wheel unit 33 has a lower pressure wheel 332 biased to move in a second direction (B) so as to press and tense a lower segment 272 of the second transmission belt 27 that extends between the flywheel unit 24 and the crank wheel unit 25 below the upper segment 271. In this embodiment, the first and second directions (A, B) are opposite to each other along an arc-shaped groove 312 that is formed in the mounting seat 31. The upper limiting member 34 is mounted to the mounting seat 31 to limit movement of the upper pressure wheel unit 32 in a direction opposite to the first direction (A), i.e., in the second direction (B). The lower limiting member 35 is mounted to the mounting seat 31 to limit movement of the lower pressure wheel unit 33 in a direction opposite to the second direction (B), i.e., in the first direction (A).

In this embodiment, the mounting seat 31 is in the form of a plate that is welded to the first support frame 23. The mounting seat 31 is provided with a pivot 311 and the arc-shaped groove 312 that is centered at an axis (X) of the pivot 311, and is further provided with two threaded tubes 313 at a back surface 314 thereof.

The upper pressure wheel unit 32 further includes an upper plate 321, a first guide axle 3222, a first projection 3223, and a first biasing member 323. The upper plate 321 is mounted pivotally to the mounting seat 31 and has a first end carrying the first guide axle 3222 to hold rotatably the upper pressure wheel 322. The first guide axle 3222 extends slidably through the arc-shaped groove 312 and is connected to the center of the upper pressure wheel 322. The first projection 3223 extends out of the arc-shaped groove 312 from the first guide axle 3222. The first biasing member 323 is an extension spring, and has opposite ends that are coupled respectively to a second end of the upper plate 321 opposite to the first end and an upper portion of the first support frame 23. The first biasing member 323 biases the upper pressure wheel 322 toward the upper segment 271 of the second transmission belt 27. In particular, the upper plate 321 is elongated. The pivot 311 of the mounting seat 31 extends through a portion of the upper plate 321 between the first and second ends.

The lower pressure wheel unit 33 further includes a lower plate 331, a second guide axle 3322, a second projection 3323, and a second biasing member 333. The lower plate 331 has a third end mounted pivotally to the mounting seat 31. The second guide axle 3322 extends slidably through the arc-shaped groove 312 and is connected to a center of the lower pressure wheel 332. The second projection 3323 extends out of the arc-shaped groove 312 from the second guide axle 3322. The second biasing member 333 is an extension spring, and has opposite ends that are coupled respectively to a fourth end of the lower plate 331 opposite to the third end and a lower portion of the first support frame 23. The second biasing member 333 biases the lower pressure wheel 332 toward the lower segment 272 of the transmission belt 27. The lower pressure wheel 332 is mounted to the lower plate 331 between the third and fourth ends. In particular, the lower plate 331 is elongated. The pivot 311 of the mounting seat 31 extends through the third end of the lower plate 331 such that the upper and lower plates 321, 331 of the upper and lower pressure wheel units 32, 33 are pivotable co-axially about the axis (X).

Each of the upper and lower limiting members 34, 35 includes a threaded shaft 341, 351 and a positioning nut 342, 352. Each of the threaded shafts 341, 351 extends threadedly through a respective one of the threaded tubes 313. The threaded shafts 341, 351 have respective ends extending to the first and second projections 3223, 3323 of the upper and lower pressure wheel units 32, 33, respectively, such that the threaded shafts 341, 351 are capable of abutting against the first and second projections 3223, 3323, respectively. The distance from the end of each of the threaded shafts 341, 351 to the respective one of the threaded tubes 313 is adjustable so as to adjust limit imposed on the movement of the respective one of the upper and lower pressure wheels 322, 332 in the arc-shaped groove 312. The positioning nut 342, 352 engages threadedly the threaded shaft 341, 351 so as to lock the threaded shafts 341, 351 against movement after the threaded shafts 341, 351 are adjusted.

Referring back to FIG. 2, the exercise machine according to the preferred embodiment further includes a second support frame 41, a rotary shaft 42, a roller unit 43, and two swing handle units 44. The second support frame 41 extends upwardly from the base 21 and forwardly of the first support frame 23 (shown in FIG. 3). The rotary shaft 42 is mounted rotatably to an upper portion of the second support frame 41. The roller unit 43 is mounted rotatably to a lower portion of the second support frame 41. The swing handle units 44 are mounted to the rotary shaft 42.

In this embodiment, the second support frame 41 includes two support rods 411 respectively disposed on opposite sides relative to the base 21, a control panel 412 disposed across uppermost ends of the support rods 411, and two handrails 413 (only one is visible in FIG. 2) respectively disposed on opposite sides of the control panel 412. Two shaft barrels 421 are provided around on the rotary shaft 42 and are respectively fixed to the swing handle units 44, such as by welding. The roller unit 43 includes a roller shaft 431 mounted to the second support frame 41 between the support rods 411 via two screw fasteners 432, and two rollers 433 coupled rotatably to the roller shaft 431.

Each of the swing handle units 44 includes a grip 441 and a swing handle 442 coupled to a respective one of the shaft barrels 421, a slide rod 443 connected telescopically to a bottom end of the swing handle 442, and a fixer knob 444 provided on the swing handle 442 for locking the slide rod 443 to the bottom end of the swing handle 442. The swing handle 442 is provided with a first ear part 445, and the slide rod 443 is provided with a second ear part 446. The slide rod 443 can be divided into three segments (or any number of segments as determined by the manufacturer) such that the length of the swing handle unit 44 is adjustable to suit users of various heights.

The pedal assemblies 50 (only one is shown in FIG. 2) are disposed on opposite sides of the first support frame 23 (shown in FIG. 3). Each of the pedal assemblies 50 includes a pedal rod 51, first and second link rod units 52, 54, and a pedal member 53. The pedal rod 51 has a forward segment in slidable contact with a respective one of the rollers 433 of the roller unit 43, and a rearward segment connected rotatably to the crank wheel unit 25 (shown in FIG. 3). The first link rod unit 52 has opposite first and second end parts that are coupled pivotally to a front end of the pedal rod 51 and a respective one of the swing handle units 44, respectively. The pedal member 53 is mounted slidably to the pedal rod 51. The second link rod unit 54 has opposite third and fourth end parts that are coupled pivotally to the pedal member 53 and the respective one of the swing handle units 44, respectively.

In this embodiment, the pedal rod 51 is a lengthy plate body with a predefined length, and is formed with slide rails 511 (only one can be seen in FIG. 2) on opposite sides thereof for mounting of the pedal member 53 slidably thereto. The pedal rod 51 is provided with a third ear part 512 at the front end. A rear end of the pedal rod 51 is coupled pivotally to one end of the respective crank 252 (shown in FIG. 3). The first and second end parts of the first link rod unit 52 are coupled pivotally and respectively to the third ear part 512 of the pedal rod 51 and the first ear part 445 of the respective swing handle 442. The pedal member 53 is a plate body that is formed with a slide seat 531 engaging slidably the slide rails 511 of the pedal rod 51, and a fourth ear part 533 at a forward end thereof. The second link rod unit 54 includes a primary rod section 541 and a secondary rod section 542 connected telescopically to each other, and a fixing knob 543 for locking the secondary rod section 542 to the primary rod section 541. A free end of the primary rod section 541 is configured as the fourth end part of the second link rod unit 54, and is coupled pivotally to the second ear part 446 of the respective slide rod 443. A free end of the secondary rod section 542 is configured as the third end part of the second link rod unit 54, and is coupled pivotally to the fourth ear part 533 of the pedal member 53. The secondary rod section 542 can be divided into three segments (or any number of segments as determined by the manufacturer) so as to provide adjustments to the position of the pedal member 53 on the pedal rod 51 such that the distance between the pedal member 53 and the grip 441 of the respective swing handle unit 44 is adjustable to suit users of various heights.

The operation of and results achieved by the exercise machine are described hereinbelow.

As shown in FIG. 7, power of the exercise machine needs to be turned on via the control panel 412 when the user wishes to perform exercise. While the electric motor 22 is running, the cranks 252 are brought into rotation such that the rear ends of the pedal rods 51 of the pedal assemblies 50, which are coupled pivotally to the cranks 252, rotate in a circle about the center of the crank wheel 251 (as shown in FIG. 3). The front end of each pedal rod 51 brings the corresponding swing handle unit 44 into swinging motion relative to the rotary shaft 42. Since each pedal member 53 is mounted slidably on the corresponding pedal rod 51, and is coupled pivotally to the corresponding second link rod unit 54, when the swing handle unit 44 swings, the corresponding pedal member 53 slides along the pedal rod 51 such that the user's leg moves in an elliptical course similar to that experienced during a running exercise.

Referring to FIG. 8 and FIG. 9, when the user pedals to rotate the crank wheel unit 25 counterclockwise such that one of the cranks 252 is moved from position (I) to position (II), the user's weight on the corresponding pedal assembly 50 exerts a force (P) on the crank 252 that tends to bring the crank wheel 251 into counterclockwise rotation. Under this situation, the lower segment 272 of the second transmission belt 27 has a tendency to become tense, while the upper segment 271 of the second transmission belt 27 has a tendency to become slack. At this time, the first biasing member 323 of the upper pressure wheel unit 32 biases the upper pressure wheel 322 toward the upper segment 271 of the second transmission belt 27 in the first direction (A) such that the upper segment 271 is maintained in a tense state. On the other hand, the already-tense lower segment 272 of the second transmission belt 27 exerts an opposing force on the lower pressure wheel 332 in the second direction (B). However, since the second projection 3323 of the lower pressure wheel unit 33 abuts against the lower limiting member 35 such that the lower pressure wheel 332 is limited in position in the arc-shaped groove 312, the tension in the lower segment 272 of the second transmission belt 27 is maintained. As a result, both the upper and lower segments 271, 272 of the second transmission belt 27 are maintained in a tense state.

Referring to FIG. 10 and FIG. 11, said one of the cranks 252 moves from the position (II) to the position (I) when the user pedals to rotate the other crank 252 from the position (I) to the position (II). At this time, when the user's weight is applied to the pedal assembly 50 corresponding to said one of the cranks 252, a force (P) is exerted on said one of the cranks 252 that tends to bring the crank wheel 251 into clockwise rotation. Under this situation, the upper segment 271 of the second transmission belt 27 has a tendency to become tense, while the lower segment 272 of the second transmission belt 27 has a tendency to become slack. At this time, the second biasing member 333 of the lower pressure wheel unit 33 biases the lower pressure wheel 332 toward the lower segment 272 of the second transmission belt 27 in the second direction (B) such that the lower segment 272 is maintained in a tense state. On the other hand, the already-tense upper segment 271 of the second transmission belt 27 exerts an opposing force on the upper pressure wheel 322 in the first direction (A). However, since the first projection 3223 of the upper pressure wheel unit 32 abuts against the upper limiting member 34 such that the upper pressure wheel 322 is limited in position in the arc-shaped groove 312, the tension in the upper segment 271 of the second transmission belt 27 is maintained. As a result, both the upper and lower segments 271, 272 of the second transmission belt 27 are maintained in a tense state.

As shown in FIG. 12, during swinging motion of the swing handle units 44, a lowermost end of each swing handle 442 brings the corresponding pedal rod 51 into motion through an interconnection established by the corresponding first link rod unit 52. The slide rod 443, which is disposed below the swing handle 442, brings the corresponding pedal member 53 into motion through an interconnection established by the corresponding second link rod unit 54. Since the swing handle 442 and the slide rod 443 both swing about the rotary shaft 42, under the same angle of rotation, the oscillating displacement experienced at lowermost ends of the swing handle 442 and the slide rod 443 are different due to their varying distance from the rotary shaft 42. Therefore, the slide rod 443 brings the corresponding pedal member 53 into a larger displacement, while the swing handle 442 brings the corresponding pedal rod 51 into a smaller displacement. Because there exists a difference between the displacements the pedal member 53 and the pedal rod 51 each experiences, while the pedal member 53 moves in an elliptical course along with the pedal rod 51, the pedal member 53 further slides along the pedal rod 51, thereby creating an increased step size during the exercise.

As described hereinabove, the main object of the present invention is to prevent slippage of the transmission belt during operation of the exercise machine. In the preferred embodiment, this is achieved by utilizing the upper and lower pressure wheels 322, 332 and the upper and lower limiting members 34, 35 to press and tense the upper and lower segments 271, 272 of the second transmission belt 27 such that no matter which direction (clockwise or counterclockwise) the crank wheel 251 rotates, tension in the second transmission belt 27 is maintained to ensure optimal operation of the exercise machine. In other words, the present invention provides thorough transmission of power in and smooth operation of the exercise machine. In addition, due to the special configuration and linkage relationships among the swing handle units 44, the rotary shaft 42, the first and second link rod units 52, 54, the pedal shafts 51, and the pedal members 53, the present invention is capable of providing an increased step-size for the user during use of the exercise machine.

While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this invention is not limited to the disclosed embodiment but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation and equivalent arrangements. 

1. An exercise machine comprising: a base; a first support frame mounted to said base; a flywheel unit mounted rotatably to said first support frame; a crank wheel unit mounted rotatably to said first support frame; a transmission belt trained on said flywheel unit and said crank wheel unit; and a pressurizing wheel mechanism including: a mounting seat mounted to said first support frame, and disposed proximate to said transmission belt; an upper pressure wheel unit provided pivotally on said mounting seat, and having an upper pressure wheel biased to move in a first direction so as to press and tense an upper segment of said transmission belt that extends between said flywheel unit and said crank wheel unit; a lower pressure wheel unit provided pivotally on said mounting seat, and having a lower pressure wheel biased to move in a second direction so as to press and tense a lower segment of said transmission belt that extends between said flywheel unit and said crank wheel unit below said upper segment; an upper limiting member mounted to said mounting seat to limit movement of said upper pressure wheel unit in a direction opposite to said first direction; and a lower limiting member mounted to said mounting seat to limit movement of said lower pressure wheel unit in a direction opposite to the second direction.
 2. The exercise machine as claimed in claim 1, wherein said upper pressure wheel unit further includes an upper plate mounted pivotally to said mounting seat and having a first end holding rotatably said upper pressure wheel, and a first biasing member coupled to a second end of said upper plate opposite to said first end for biasing said upper pressure wheel toward said upper segment of said transmission belt.
 3. The exercise machine as claimed in claim 2, wherein said lower pressure wheel unit further includes a lower plate having a third end mounted pivotally to said mounting seat, and a second biasing member coupled to a fourth end of said lower plate opposite to said third end for biasing said lower pressure wheel toward said lower segment of said transmission belt, said lower pressure wheel being mounted to said lower plate between said third and fourth ends.
 4. The exercise machine as claimed in claim 3, wherein said upper and lower plates are pivotable co-axially about an axis on said mounting seat, said mounting seat being formed with an arc-shaped groove that is centered at said axis; and each of said upper and lower pressure wheel units includes a guide axle extending slidably through said arc-shaped groove and connected to a respective one of said upper and lower pressure wheels, and a projection extending out of said arc-shaped groove from said guide axle, each of said upper and lower limiting members being capable of a butting against said projection of a respective one of said upper and lower pressure wheel units so as to limit pivoting movement of the respective one of said upper and lower pressure wheels.
 5. The exercise machine as claimed in claim 1, wherein said mounting seat is provided with two threaded tubes, each of said upper and lower limiting members including a threaded shaft that extends threadedly through a respective one of said threaded tubes, and that is capable of abutting against a respective one of said upper and lower pressure wheel units, and a positioning nut that engages threadedly said threaded shaft so as to prevent said threaded shaft from moving relative to the respective one of said threaded tubes.
 6. The exercise machine as claimed in claim 1, further comprising: a second support frame extending upwardly from said base and forwardly of said first support frame; a rotary shaft mounted rotatably to an upper portion of said second support frame; a roller unit mounted rotatably to a lower portion of said second support frame; two swing handle units mounted to said rotary shaft; and two pedal assemblies disposed on opposite sides of said first support frame, and each including: a pedal rod having a forward segment in slidable contact with said roller unit, and a rearward segment connected rotatably to said crank wheel unit, a first link rod unit having opposite first and second end parts that are coupled pivotally to a front end of said pedal rod and a respective one of said swing handle units, respectively, a pedal member mounted slidably to said pedal rod, and a second link rod unit having opposite third and fourth end parts that are coupled pivotally to said pedal member and the respective one of said swing handle units, respectively.
 7. The exercise machine as claimed in claim 6, wherein said roller unit includes a roller shaft mounted to said second support frame, and two rollers coupled rotatably to said roller shaft, each of said rollers being in slidable contact with said forward segment of said pedal rod of a respective one of said pedal assemblies.
 8. The exercise machine as claimed in claim 6, wherein each of said swing handle units includes a swing handle, a slide rod connected telescopically to a bottom end of said swing handle, and a fixer knob provided on said swing handle for locking said slide rod to said bottom end, said swing handle being coupled pivotally to said second end part of said first link rod unit of the respective one of said pedal assemblies, said slide rod being coupled pivotally to said fourth end part of said second link rod unit of the respective one of said pedal assemblies.
 9. The exercise machine as claimed in claim 6, wherein said second link rod unit includes a primary rod section and a secondary rod section connected telescopically to each other, and a fixing knob for locking said secondary rod section to said primary rod section.
 10. The exercise machine as claimed in claim 1, further comprising an electric motor mounted to said base, disposed forwardly of said first support frame, and coupled to said flywheel unit for providing a driving force to drive said flywheel unit.
 11. An exercise machine comprising: a base; a first support frame mounted to said base; a flywheel unit mounted rotatably to said first support frame; a crank wheel unit mounted rotatably to said first support frame; a transmission belt trained on said flywheel unit and said crank wheel unit; and a pressurizing wheel mechanism including: a mounting seat mounted to said first support frame, and disposed proximate to said transmission belt; a pressure wheel unit provided pivotally on said mounting seat, and having a pressure wheel biased to move in a first direction so as to press and tense a segment of said transmission belt that extends between said flywheel unit and said crank wheel unit; and a limiting member mounted to said mounting seat to limit movement of said pressure wheel unit in a direction opposite to said first direction.
 12. The exercise machine as claimed in claim 11, further comprising an electric motor mounted to said base, disposed forwardly of said first support frame, and coupled to said flywheel unit for providing a driving force to drive said flywheel unit.
 13. An exercise machine comprising: a base; a first support frame mounted to said base; a flywheel unit mounted rotatably to said first support frame; a crank wheel unit mounted rotatably to said first support frame; a transmission belt trained on said flywheel unit and said crank wheel unit; and a pressurizing wheel mechanism including: a mounting seat mounted to said first support frame, and disposed proximate to said transmission belt; an upper pressure wheel unit provided pivotally on said mounting seat, and having an upper plate holding an upper pressure wheel biased to move in a first direction so as to press and tense an upper segment of said transmission belt that extends between said flywheel unit and said crank wheel unit; and a lower pressure wheel unit provided pivotally on said mounting seat, and having a lower plate holding a lower pressure wheel biased to move in a second direction so as to press and tense a lower segment of said transmission belt that extends between said flywheel unit and said crank wheel unit below said upper segment.
 14. The exercise machine as claimed in claim 13, wherein said upper and lower plates are mounted coaxially on said mounting seat to rotate about an axis.
 15. The exercise machine as claimed in claim 14, wherein said mounting seat has an arc-shaped groove centered at said axis.
 16. The exercise machine as claimed in claim 15, wherein said upper and lower wheels are movable in a direction along said arc-shaped groove.
 17. The exercise machine as claimed in claim 16, further comprising an electric motor mounted to said base, disposed forwardly of said first support frame, and coupled to said flywheel unit for providing a driving force to drive said flywheel unit. 